Start with first reflection points
The strongest early reflections come off the surfaces where sound bounces once on its way from a speaker to your head — typically the side walls, and often the ceiling. The classic way to find them: have a friend slide a mirror along the wall while you sit in your listening spot; wherever you can see a speaker in the mirror is a reflection point. That's where a panel earns its keep.
Diffuse the rear wall
The wall behind the listener is a favourite spot for diffusion. A 1D or 2D diffuser there scatters the back reflection so it returns as a sense of spaciousness rather than a distinct slap echo — you keep the room's life without the smear.
Diffuser or absorber at each spot?
- Side-wall first reflections → absorber for a tight, dry mix position; diffuser to keep it lively
- Rear wall → diffuser (scatter the return), or absorber in a small room
- Ceiling above the listener → 2-D diffuser cloud, or an absorber
- Corners → bass trapping (absorption), not diffusion
Not sure which panel a spot wants? Read diffuser vs absorber first, then design the panel and it'll size itself to your wall.